This work aimed to contribute to knowledge improvement of the great Lake ecosystems of Chad, precisely that of the Lakes of Ounianga using bathymetric statements on water levels and the in situ analysis of physicochemical parameters of the lake’s waters. Bathymetric surveys facilitated characterization of the morphology of the bottom of the lakes with depths that vary from 0 to -27 m and 0 to -5.7 m for Yoan and Teli Lakes, respectively. With regards to water physio-chemistry, the temperature of the Teli Lake water measuring up to 0.5 m varied from 20.8 to 36°C, while that of Lake Yoan varied from 10.50 to 32.90°C, with an average of 22 and 27°C. The conductivity values oscillated between 69 and 111,700 μS/cm for the Lake Teli and 100 to 64,000 μS/cm for the Lake Yoan. This document illustrates the techniques used in the investigation of a lake whose study constitutes a wide field of continental hydrology.